chain id

[lukeiannucci]

Closes #<ISSUE_NUMBER>

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[gemini-code-assist]

Code Review

This pull request introduces a ChainId field to the EspressoState struct and updates NewEspressoStore to accept a namespace parameter (representing the chain ID) to initialize this field. Additionally, both the Nitro and OP verifiers are updated to validate that the chain ID retrieved from the L2 client matches the ChainId stored in the state file. The review feedback highlights a critical backward compatibility issue where loading legacy state files (which lack chain_id) will result in a ChainId of 0, causing the verifier's check to fail and crash the proxy. To address this, the reviewer suggests a migration path in NewEspressoStore, along with a corresponding unit test and minor typo corrections in log messages.

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[jjeangal]

Lgtm.